By Shankar Vedantam
Washington Post Staff Writer
Tuesday, September 5, 2006
Children born to fathers of advancing age are at significantly higher risk of developing autism compared with children born to younger fathers, according a comprehensive study published yesterday that offers surprising new insight into one of the most feared disorders of the brain.
The finding comes at a time of great controversy over autism in the United States, as a recent surge in diagnoses has fueled speculations about various possible causes of the disorder. For scientists, both the origins of and potential treatments for the disorder remain a mystery.
With every decade of advancing age starting with men in their teens and twenties, the new study found, older fathers pose a growing risk to their children when it comes to autism -- unhappy evidence that the medical risks associated with late parenthood are not just the province of older mothers, as much previous research has suggested.
Of special concern is the finding that the risk for autism not only increases with paternal age but also appears to accelerate.
When fathers are in their thirties, children have about 1 1/2 times the risk of developing autism of children of fathers in their teens and twenties. Compared with the offspring of the youngest fathers, children of fathers in their forties have more than five times the risk of developing autism, and children of fathers in their fifties have more than nine times the risk.
Autism is a developmental disorder that is often characterized by social and verbal problems. It becomes manifest early in childhood and is associated with learning deficits and other problems. Many cases are diagnosed shortly after children enter school, where differences among kids become too obvious to ignore.
A wide variety of interventions are increasingly available for autistic children, and early behavioral interventions have been said to help with outcomes and functioning. There is, however, no cure for the disorder, and scientists are not sure about its biological roots.
The new study presents an intriguing new avenue for research, because it suggests that genetic traits passed along by fathers, as opposed to mothers, may play some significant role in creating susceptibility to autism. Several other studies have suggested that older parents of both sexes are at greater risk of having children with developmental disorders. Three earlier studies looking at the relationship between paternal age and autism have produced mixed results; the new study is the most rigorous analysis conducted to date.
The study was based on an enormous sample of 17-year-olds -- nearly all the male and three-quarters of the female subjects of that age found over a six-year period in Israel, as they came of draft age. In all, data from 378,891 people were analyzed.
Since all Israeli citizens have a unique identification number, and the draft process routinely calls for listing the identification numbers of parents, researchers were able to develop a large-scale map that allowed them to determine the age of both parents for 132,271 draft candidates. They then compared that information against medical evaluations conducted by the draft board for autism and other disorders for those same candidates.
Abraham Reichenberg at the Mount Sinai School of Medicine in New York, along with several others at research institutions in the United States and Israel, found a significant relationship between paternal age and autism, even after accounting for other factors, such as mothers' age and socioeconomic status.
Children of fathers who were 15 to 29 years of age had a risk of about six in 10,000 of developing autism. Children of fathers in their thirties had a risk of nine in 10,000. Children of fathers in their forties had a risk of 32 in 10,000, and children of fathers who were older than 50 had a risk of 52 in 10,000.
In a paper published yesterday in the Archives of General Psychiatry, the researchers said that the number of cases of autism among families with the oldest dads was too small to lead to definitive conclusions about that group, but that there was little doubt about the overall trend. The only question, they said, is whether the risk accumulates at an accelerating rate with advancing paternal age, as the numbers in this study suggest.
Scientists in the United States are increasingly thinking about autism in terms of a spectrum of problems, which is why they have coined the term "autism spectrum disorders." The federal government estimates that the risk for autism spectrum disorders in the United States is around 3.4 for every 1,000 children between the ages of 3 and 10.
Whether that number is on the rise has been hotly contested; better outreach and diagnostic efforts may be finding children who would previously have gone undetected. Enduring disparities in access to health care complicate the picture. While the medical complexities of autism are present in Israel, concern over disparities is mitigated to some extent because Israel has universal health insurance, which guarantees equal access to care.
The Israeli military draft board's medical diagnostic system does not differentiate among conditions on the autism spectrum, which includes autism, Asperger's syndrome, Rett syndrome and what are known as pervasive developmental disorders.
Autistic people can be unresponsive in social situations, or focused intently on a single task or object for long periods. While some parents recognize that their babies seem different from a very young age, U.S. government researchers also say that sometimes engaging and babbling babies can suddenly turn "silent, withdrawn, self-abusive, or indifferent to social overtures."
In recent years, concern and controversy have grown -- despite a lack of conclusive evidence -- that mercury in children's vaccines produces toxicity that leads to autism.
While the link between older fathers and autistic children is likely to be genetic, the researchers who conducted the new study also acknowledged the possibility that unknown other factors could simultaneously be causing men to delay parenthood while independently increasing autism rates.